redefine – Conditional macro, etc., definitions

De­fines com­mands \newdef, \newgdef and
\newlet that warn the user if a com­mand is re­de­fined
us­ing them (if op­er­at­ing un­der LaTeX, \new­com­mand is
sim­i­larly mod­i­fied). In ad­di­tion \newif,
\new­box, \new­count, \newdi­men,
\new­toks are mod­i­fied to de­tect an er­ror if a con­di­tional
or reg­is­ter name is reused.